in retrospect this solution is completely obvious but i thought i would mention it in case somebody searches for it.
in agenda, i do c-u c-u c-d. this allows me to remove deadline warning days [RET, very convenient!] or specify them. a good thing about this feature is that there is less chance of manually creating a format error in the timestamp as would occur by going to the ts and editing it manually. also it seems nothing is relative to the existing warning. that is good. the prompt, however, seems geared toward specifying a date. you can specify indirectly the deadline warning days by specifying the date that would be the warning. the question is, can we specify deadline warning days directly? here is where it is obvious in retrospect but as i was not thinking in terms of default date it was not. suppose i want deadline warning days of -2d but do not want to manually edit the ts or calculate the corresponding date. if the deadline is somewhat in the future but displayed in the deadline section of the agenda, and i try c-u c-u c-d, the following intuitive ideas do not work: 2, -2, 2d, -2d, and as desperation, trying the in retrospect nonsensical . first. i wasn't fully cogitating that the prompt was date oriented but that the default date is the ts date and can work. i read the manual for my obsolete version of org (info "(org) The date/time prompt") and my brain did not find it. i was looking at the examples for things like -- even though they were mentioned in the text. solution seems to be --2d. whether modern org needs to include a few examples with -- or not, idk. idk if that helps anybody [it is going to take much time to upgrade].